Study On Dynamic Characteristics Of Soil CO₂Fluxes And Factors In Different Land Use Types

Green house has become the most popular issues at present. The studiesconcerning the interchange of greenhouse gas between terrestrial ecosystems andatmosphere under the interference of human-being are becoming increasingly popular.The impacts of soil respiration which is considered as one of crucial links on thebalance of global contents of carbon element is a hot topic in the world. And moisture,temperature and vegetation condition are important influencing factors related to soilrespiration. Daqing locates west northern in Jilin province. This area is classifiedecologically fragile zone, and is sensitive to the variations of global changes. Thiszone is belonging to developing areas in China. Thus, the characteristic of this area isthe hysteresis of economical status and rapid deterioration of ecological environment.Therefore, there is significance studying the dynamic traits of soil respiration underdifferent utilization patterns.This thesis is based on the natural science foundation project called “the impactsof LUCC on the organic carbon of soil and their mechanisms”. The experiment isdevised through soil survey data, satellite remote sensing images, meteorological dataand, the underlying data source, such as thematic graphics. The main experimentalprocess include the dynamic character of soil respiration, the determination oftemperature, moisture and organic carbon in soil, the contents of hydrolysable N, andthe activity of soil enzyme. The impact of these factors on the soil respiration hasbeen analyzed after the determination.First of all, the method of in situ determination and apparatus of ratios of soilrespiration are introduced methodically. On this basis, day and seasonal dynamics ofsoil respiration in four types of land use comprising paddy field, dry land, grass landand saline-alkali land were determined. The result indicated that the soil respiration ofunder land use appeared as the way of “a single peak curve”, and there weresignificant diversities among ratios of respirations under different conditions of landuse. The specific difference of the ratios was paddy land> grass land> saline-alkali land> dry land. The day average ratios of all the soil respiration were similar to theratios of soil respiration which were measured at10:00. Thus, the day average ratiosof soil respiration could be appraised by the value at10:00. The result of seasonaldynamic of soil respiration also showed that soil respiration under different conditionsappeared the variation of multi-peak curve. The main tendency was that the ratios ofsoil respiration increased gradually since May, and achieved maximum in late July orAugust, and then decreased by degrees. The descending order of the rates ofvariations of soil respiration was: grass land, dry land, paddy land and saline-alkaliland. The descending order of seasonal average value of soil respiration was: grassland, paddy land, dry land and saline-alkali land.Moreover, the main factors affecting soil respiration and the method ofdetermination were studied. And then the different factors affecting soil respirationunder4land utilizations are measured through the comparison between the datarelated to these factors to the values of respirations. The results of soil respirationaffected by temperature was carried out that the variation lagged behind thediversification of the climate but were consistent with the variations of soiltemperature. This phenomenon is mainly resulted from the indirect impact of climatechanges on the soil temperature, which influence the soil respiration then. During thecorrelation analysis, the day variation of ratios of respiration in paddy land had themost significant correlation with the temperature (R2=0.8375), followed by dry landand grass land. However, the descending order of the correlation between soilrespiration and temperature of surface soil under4land use is different from that ofthe temperature. This phenomenon may be due to other factors.Furthermore, the impacts of moisture on soil respiration under different land useswere studied. This part of result discovered that there were insignificant relationsbetween soil respiration and moisture contents of soil, the range of R2was0.0022-0251. This insignificance may related to climate of Daqing zone. Thecorrelation between the moisture contents of soil and soil respiration was inferior tothe relationship between temperature of surface soil and soil respiration. That is to saythat, the impact of temperature on the soil respiration was greater than that of moisture contents of soil on soil respiration. At the same time, the impact ofcomprehensive utilization of water and heat on the soil respiration was studied. Theresult illustrated that complex model between soil respiration and factors, includingtemperature of soil and moisture, could explained regulation of soil respiration. Themoisture and temperature at10cm on the soil surface could depict the65.47%soilrespiration of paddy land,76.25%soil respiration of dry land,82.17%soil respirationof grass land and57.62%soil respiration of saline-alkali land. Thus, this complexmodel can fitted well with the kinetic variations of soil respiration.Finally, the impacts of other factors (organic carbon of soil, hydrosable N andviability of enzyme of soil) on the day variations of respiration were determined. Thestudy found that organic carbon and hydrosable N were distinct respectively underdifferent land use. the activities among catalase, dehydrogenase and polyphenoloxidase. The descending order of contents of organic carbon under different land usewas: paddy land>dry land> grass land> saline-alkali land. The contents of hydrosableN was grassland> paddy land> dry alnd> saline-alkali land. There were significantdifference between carbon and nitrogen of soil under different land use, saline-alkaliland> paddy land> dry land> Grass land.